Homework Help: Bullet in water

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1. Jul 29, 2015

Neil B

< Mentor Note -- OP has been reminded to use the HH Template and show their work in future posts... >

A man fires a bullet into a swimming pool.

There is a distance of 6m from the gun to the bottom of the pool.

Does the bullet have enough force through the water to break an average bike chain - which is holding a person captive to the bottom.

(Obviously this is more about believability in energy dispersion than ultra accurate measurements)

Last edited by a moderator: Jul 29, 2015
2. Jul 29, 2015

Dr. Courtney

Bullets lose most or all of their kinetic energy in the first 30-100 cm of water. Handgun bullets don't have much left after 30 cm. A pointy rifle bullet that does not tumble may have a tiny bit of energy left after penetrating 100 cm of water.

3. Jul 29, 2015

davenn

Mythbusters did an episode on this and found as Dr Courtney has said, the projectiles don't travel very far into the water and the projectiles tended to break up ( angle of penetration of the projectile into the water has some effect)

The tried hand guns, rifles and even a hi powered 50 calibre gun, the effect was pretty much the same for all of them

http://www.bing.com/videos/search?q=mythbusters,+firing+guns+into+pool&FORM=VIRE1#view=detail&mid=D76E9A00B7A63A7A9A16D76E9A00B7A63A7A9A16

cheers
Dave

Last edited: Jul 30, 2015
4. Jul 29, 2015

Dr. Courtney

I love Mythbusters and their enthusiasm for experimental approaches to questions. But, I'm not sure I would cite their episodes as reliable answers. They did get this one right though, and it was a great episode. One of the project ideas I like to pose to students is picking 10 mythbuster episodes, designing experiments to test the same questions they test, and seeing how many of the 10 experiments yield the same answers.

5. Jul 29, 2015

Staff: Mentor

What is the verification percentage? I'm curious...

6. Jul 29, 2015

Dr. Courtney

Me too. Unfortunately, our students keep picking projects more likely to yield peer-reviewed publications and win science fairs instead of the really interesing ones like testing Mythbusters accuracy percentage. I would guess 70-90% (based on my experience in overlapping areas like blast and ballistics.)

7. Jul 30, 2015

insightful

To clarify, it was a .50 caliber (0.5 inch diameter bullet) gun, not a 50mm, which is a cannon (MUCH bigger weapon).

8. Jul 30, 2015

davenn

thanks for pointing out my type :)

will correct